S U M M A R YP-Lactamases (EC. 3 . 5 . 2 . 6 ) from strains of Gram-negative bacteria have been studied using analytical isoelectric focusing. This permits a visual comparison of the patterns of P-lactamase bands produced by enzymes from different organisms. Purification of crude intracellular preparations is unnecessary and the technique is sufficiently sensitive to demonstrate P-lactamase in mutants previously reported to lack the enzyme. R factor RTEM and RPI P-lactamases that have not been distinguished from one another biochemically or immunologically can be differentiated by isoelectric focusing. Conversely, the enzymes specified by the R factors RTEM, R I and RGNI1, with identical isoelectric focusing patterns, have the same biochemical properties. Chromosomal and R factor-mediated P-lactamases from single strains have been separated and their identities confirmed by immunoisoelectric focusing, R factor-mediated enzymes gave identical isoelectric focusing patterns irrespective of the host strain. Isoelectric focusing can therefore be used to observe the transfer of P-lactamases carried by R factors. I N T R O D U C T I O NIsoelectric focusing (Haglund, 1967) is a method of separation in which proteins align themselves as sharp bands at their isoelectric points (PI) in an electrophoretically-produced pH gradient. A high degree of resolution is obtained by the method, because focusing is caused by forces that act against diffusion and proteins are therefore concentrated during their separation. We have used the technique in the analytical mode for the separation of P-lactamases (EC. 3 . 5 . 2 . 6 ) on thin layers of polyacrylamide gel and have located the focused enzymes with a cephalosporin substrate which changes colour after degradation by P-lactamase. This technique of separation and specific staining of P-lactamases allows demonstration of low levels of activity and presents the different enzymes produced by various strains as patterns of bands that can easily be recognized and compared.The P-lactamases produced by Gram-negative bacteria are known to differ in their substrate specificities, inhibitor profiles, electrophoretic mobilities, biochemical properties and reactions with antisera ( Yamagishi et al. 1969). These enzymes have frequently been classified by the relative rates at which they hydrolyse penicillins and cephalosporins. Various methods have been used for estimating the activity of crude and pure enzyme preparations, and when a single strain produces two P-lactamases these have not always been separated before determining the substrate profile. Comparison of profiles determined in different laboratories may therefore be misleading. The use of isoelectric focusing of P-lactamases for direct comparison of different enzymes has been illustrated in this paper principally by reference to enzymes from Escherichia coli. This species was chosen because strains carrying R factors specifying well-characterized P-lactamases were available. METHODSStrains. These are listed in Table I. The clinical ...

BackgroundMedical school attrition is important - securing a place in medical school is difficult and a high attrition rate can affect the academic reputation of a medical school and staff morale. More important, however, are the personal consequences of dropout for the student. The aims of our study were to examine factors associated with attrition over a ten-year period (2001–2011) and to study the personal effects of dropout on individual students.MethodsThe study included quantitative analysis of completed cohorts and qualitative analysis of ten-year data. Data were collected from individual student files, examination and admission records, exit interviews and staff interviews. Statistical analysis was carried out on five successive completed cohorts. Qualitative data from student files was transcribed and independently analysed by three authors. Data was coded and categorized and key themes were identified.ResultsOverall attrition rate was 5.7% (45/779) in 6 completed cohorts when students who transferred to other medical courses were excluded. Students from Kuwait and United Arab Emirates had the highest dropout rate (RR = 5.70, 95% Confidence Intervals 2.65 to 12.27;p < 0.0001) compared to Irish and EU students combined. North American students had a higher dropout rate than Irish and EU students; RR = 2.68 (1.09 to 6.58;p = 0.027) but this was not significant when transfers were excluded (RR = 1.32(0.38, 4.62);p = 0.75). Male students were more likely to dropout than females (RR 1.70, .93 to 3.11) but this was not significant (p = 0.079).Absenteeism was documented in 30% of students, academic difficulty in 55.7%, social isolation in 20%, and psychological morbidity in 40% (higher than other studies). Qualitative analysis revealed recurrent themes of isolation, failure, and despair. Student Welfare services were only accessed by one-third of dropout students.ConclusionsWhile dropout is often multifactorial, certain red flag signals may alert us to risk of dropout including non-EU origin, academic struggling, absenteeism, social isolation, depression and leave of absence. Psychological morbidity amongst dropout students is high and Student Welfare services should be actively promoted. Absenteeism should prompt early intervention. Behind every dropout statistic lies a personal story. All medical schools have a duty of care to support students who leave the medical programme.

SUMMARYP-Lactamases (EC. 3.5.2.6) can be directly compared by analytical isoelectric focusing. Using this technique, 242 strains from five Gram-positive and 16 Gramnegative genera were examined. A preparation of each strain focused as a single group of bands which did not match the pattern of any R factor-associated P-lactamase. None of the strains was known to carry an R factor and resistance transfer experiments were unsuccessful. The enzymes studied were therefore thought to be chromosomally mediated. The isoelectric points ranged from 3-9 to 8-7 and were not related to the substrate profiles or other biochemical properties. The chromosomal P-lactamases appeared to be specific for genus, species and sub-species, and strains that produced identical P-lactamases had identical bacterial characteristics. Correlation of bacteriological differences with differences in ,8-lactamase patterns is discussed with particular reference to strains of Escherichia coli and Klebsiella spp. Since P-lactamases may be universally produced by bacteria, separation of the enzymes by analytical isoelectric focusing could be used in bacterial taxonomy. I N T R O D U C T I O N@-Lactamases that cannot be distinguished biochemically and immunologically can be differentiated by analytical isoelectric focusing (Matthew et al., 1975). Using this very sensitive technique, the different enzymes produced by various strains each appear as a pattern of bands (usually a group comprising a main band and satellites) which can be compared visually. Chromosomal and R factor-mediated P-lactamases produced by a single strain appear as separate entities and two groups of bands have always been seen in the isoelectric focusing patterns of 175 strains known to carry transmissible R factors mediating resistance to P-lactam antibiotics (Matthew ef al., 1975; and unpublished observations). Each strain described in this paper produced P-lactamase that focused as a single group of bands. We believe that all these P-lactamases are specified by the bacterial chromosome, and we present evidence that the enzymes are specific for genus, species and sub-species. Since the grouping of organisms by their P-lactamase patterns correlates with conventional taxonomic grouping, comparison of chromosomally-mediated P-lactamases may be used as a single criterion for assigning strains to sub-species delineated by combinations of other available tests. METHODS

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A study of responses by Culicoides spp. to light traps with light-emitting diodes (LEDs) confirmed that the livestock virus vector, Culicoides brevitarsis Kieffer, was preferentially attracted to green light. Four species shown previously to respond to blue light exhibited significantly higher responses to ultraviolet (UV) light. Field trials comparing green LEDs with incandescent lights in New South Wales, Northern Territory and East Timor confirmed the superiority of green LEDs for catching C. brevitarsis. The green LED traps also had a significant advantage over incandescent traps for a wide range of Culicoides species. These included: species whose ultimate preference was for UV, most species that are proven or potential vectors of viruses affecting Australian livestock and native animals and the main species affecting humans in northern Australia. Use of green LEDs has been adopted for trapping C. brevitarsis, especially in its marginal and low-density areas, and for detecting incursions of new Culicoides spp. into Australia. Use could be possible for species in other insect Orders.